Engines with turbochargers may use active control of the turbocharger, such as via a wastegate, intake throttle, a compressor bypass, etc., to improve engine performance and thus vehicle driveability.
Various approaches are known for controlling such engine systems based on a desired throttle inlet pressure (TIP), where the throttle inlet pressure is downstream of the turbocharger compressor, and upstream of the throttle, in the engine air inlet. However, the inventors herein have recognized limitations with such approaches.
One example approach requires that the throttle be fixed at wide open when performing boost control with the wastegate. As such, this approach eliminates the potential disturbances from the throttle, at the expense of performance and driveability improvements that can be gained by using the faster throttle controller to manage engine airflow. With the throttle disturbances eliminated, TIP feedback may be more consistent, but with a slower response time and increased error. This approach also results in a reduced loss across the throttle, which is beneficial for steady-state fuel economy.
Another example approach requires TIP to be scheduled higher than necessary to achieve a desired airflow and reduce the magnitude of throttle disturbances on TIP. This approach does not solve the TIP control issues, but manages them at the expense of steady-state fuel economy because of persistent losses across the throttle that are required to provide this partial insulation of TIP from throttle disturbances. This approach does, however, offer potential driveability and response benefits due to always intending to have excess pressure upstream of the throttle (with a fuel economy penalty).
The apparent paradox between achieving high steady state fuel economy and improved driveability may be at least partially addressed by a method of controlling a turbocharged engine having a throttle and an adjustable turbocharger (e.g., via a wastegate, variable geometry, variable nozzle, etc.) One example method comprises, moving the throttle during boosted conditions, separating out effects on the throttle inlet pressure into a first portion corresponding to disturbances caused by the movement of the throttle, and a second, remaining, portion, and adjusting the turbocharger based on the second portion and not the first portion.
In this way, it is possible to enable concurrent throttle and turbocharger control for controlling overall engine airflow and torque output, while still enabling the reduced fuel economy and improved driveability. For example, because movement of the throttle can be used, at least under some conditions, to control engine airflow during boosted conditions, it is possible to retain faster torque increases during such conditions, since boost can be maintained. In other words, torque can be temporarily reduced by reducing opening of the throttle while maintaining the turbocharger operation (e.g., without increasing opening of the wastegate), so that when the throttle opening increases, boost is already present and a rapid torque increase is achieved.
In another embodiment, the method comprises, during a boosted condition, adjusting the throttle, and during said boosted condition, adjusting the turbocharger in response to a desired turbocharger power, and an actual turbocharger power trajectory and speed trajectory, including turbocharger acceleration.
In this way, it is possible to structure a control of the turbocharger and engine airflow so that both throttle adjustment and turbocharger adjustment is coordinated to one another and do not counteract each other.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.